It seems maybe you’re actually misunderstanding. As I mentioned above, both you and the other commenter are certainly correct that the surrounding atmosphere (water in your case) exerts force on the objects as they fall, with varying effects depending on object density. However, if you take two objects that have vastly more density than the water (let’s say a big tungsten rod and another tungsten rod that has a hollow core), they will drop at approximately the same rate in the water even if their density vs each other varies. The greater the difference of their density versus the density of the medium, the less the effect of the medium. Is there still technically an effect? Sure, but that effect is negligible from a human perceptual perspective.